Evaluation of orthodontic mini-implant placement: a CBCT study ...

Kalra et al. Progress in Orthodontics 2014, 15:61http://www.progressinorthodontics.com/content/15/1/61

RESEARCH Open Access

Evaluation of orthodontic mini-implant placement:a CBCT studyShilpa Kalra*, Tulika Tripathi, Priyank Rai and Anup Kanase

Abstract

Background: Optimal positioning of orthodontic mini-implants is essential for a successful treatment with skeletalanchorage. This study aims to compare the accuracy of two-dimensional radiographs with a cone beam computedtomography (CBCT) for mini-implant placement.

Methods: An ideal site for mini-implant placement at the buccal interradicular space between the second premolarand the first molar was determined for 40 sites (in 13 patients aged 14 to 28 years) by using CBCT data. The mini-implantplacement procedure was then divided into two groups. In CBCT group, mini-implants were placed at the sitesdetermined from CBCT data. In RVG group, mini-implants were placed with the help of two-dimensional digitalradiographs and a custom made guide. Postplacement CBCT scans were obtained to determine the accuracy ofthe mini-implant placement. The results were statistically analyzed with a Mann-Whitney test.

Results: A statistically significant difference (p value = 0.02) was observed between the two groups for deviation froman ideal height of placement of the mini-implants. Deviations in mesiodistal positioning and angular deviation showeda statistically non-significant difference. Three out of twenty mini-implants in the RVG group showed root contact inthe mandibular arch that may be attributed to the narrower interradicular space and reduced accessibility in themandibular posterior region.

Conclusions: Although CBCT provides an accurate three-dimensional visualization of the interradicular space, thetwo-dimensional intraoral radiograph of the interradicular area provides sufficient information for mini-implantplacement. Considering the amount of radiation exposure and cost with the two techniques, it is recommendedto use two-dimensional radiographs with a surgical guide for a routine mini-implant placement.

Keywords: CBCT; Digital RVG; Mini-implant

BackgroundThe use of orthodontic mini-implants as an absolute an-chorage device has seen a marked increase in orthodontictreatment [1,2]. Despite their advantages over the extra-oral anchorage methods, mini-implants can occasionallyloosen during treatment and eventually fail to providefirm anchorage [3-5]. A study showed that the rates ofmini-implant failure vary between 11% and 30% [6].The two major factors that clinicians should consider

for mini-implant placement are safety and stability.Safety is related to avoiding root damage during implantplacement in the interradicular space. Stability, especiallyinitial stability, which plays a major role in preventing

* Correspondence: [email protected] of Orthodontics and Dentofacial Orthopaedics, Maulana AzadInstitute of Dental Sciences, New Delhi 110002, India

© 2014 Kalra et al.; licensee Springer. This is anAttribution License (http://creativecommons.orin any medium, provided the original work is p

premature loosening of mini-implants, is obtained byplacing the mini-implants in the alveolar bone withsufficient quantity and quality [3,7].Fayed et al [8] suggested that the optimal sites for mini-

implant placement are between the second premolar andfirst molar and between the first and second molars at thebuccal aspect of the posterior region of both jaws. Success-ful placement of mini-implants at the desired site is criticalfor their incorporation into the clinical practice. Kim et al[9] presented a surgical guide system that used cone beamcomputed tomography (CBCT) images to replicate thedental models. Surgical guides for the proper positioning oforthodontic mini-implants were fabricated on the replicasand used for precise placement. Liu et al [10] introduced aCAD/CAM template with preoperative simulation fororthodontic miniscrew placement. Similarly, other authors

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Figure 1 Orthodontic arch wire in second premolar and firstmolar region taken as standard reference for measurements.(a) Panorex View of CBCT image, (b) correlated clinically, and(c) various heights from the arch wire within the limits of mucogingivaljunction selected for bone measurements.

Figure 2 Bone measurements. (a) Mesiodistal distance, (b) buccalcortical bone thickness, (c) buccolingual thickness, and (d) bone density.

Kalra et al. Progress in Orthodontics 2014, 15:61 of 9http://www.progressinorthodontics.com/content/15/1/61

have reported the extensive use of three-dimensional plan-ning with the help of surgical guides, stents, and templatesfor accurate mini-implant positioning [11,12]. AlthoughCBCT provides additional diagnostic and therapeutic in-formation, it exposes the patients to a higher level of radi-ations than the conventional radiographs [13-15]. Thus,there is a need to assess whether the use of such an expen-sive and laborious procedure is required or not.

Figure 3 Determination of the point of entry of mini-implantby using CBCT data. (a) A perpendicular is dropped from idealpoint of insertion of mini-implant to the arch wire. (b) Distance ofpoint of intersection of perpendicular on the arch wire to distal endof second premolar bracket.

Figure 4 Custom made guide in second premolar and the firstmolar region. As seen (a) clinically and (b) radiographically.

Figure 5 Height of mini-implant from arch wire.


However, most clinicians routinely place mini-implantswithout 3D planning and use the two-dimensional radio-graphs for presurgical treatment planning. In an effort tominimize insertion errors, several innovative surgicalguides have been used which help in avoiding root injuryand subsequent patient discomfort [16-20].Despite the extensive use of two-dimensional radiographs

for mini-implant placement, little has been recorded inliterature to determine their accuracy for site selection andposition of mini-implants thereafter.The present study was aimed at evaluating the accuracy

of two-dimensional radiographs for site selection andorthodontic mini-implant placement.

MethodsThe present study evaluated 40 mini-implant placementsites in 13 patients (10 females and 3 males) aged between14 and 28 years from North Indian population group whoreported for orthodontic treatment to the Department ofOrthodontics, Maulana Azad Institute of Dental Sciences,Delhi. The included cases required the extraction of theupper and/or lower first premolars with high anchorage

consideration and were represented by eight class I biden-toalveolar protrusion patients, four class II division 1 mal-occlusion patients, and one class III surgical case. Twenty-four mini-implants (1.5 × 9 mm Infinitas mini-implant sys-tem, DB Orthodontics Limited, West Yorkshire, UK) wereplaced in the maxillae and sixteen in the mandible. Thestudy was sanctioned by the Institutional Ethics Committeeand informed consent was obtained from all the patients/

Figure 6 The post insertion measurements. (a) Deviation of thepoint of entry of the mini-implant (DMEP). (b) Deviation of the tip ofmini-implant (DMT). (c) Angular deviation of path of mini-implant (DMA).(d) Root proximity to the mini-implant.


guardians of the patients. The patients who agreed to haveCBCT scans prior to and after mini-implant placementwere included in the study. Pre- and postplacement CBCTscans were taken at an interval of 3 months. Patients withmixed dentition, missing teeth, severe periodontitis, andsystemic diseases contraindicating the procedure wereexcluded.The study design was randomized block design in which

the 40 sites (sample units) were first grouped as 20 pairs(left and right interradicular sites in the same arch in apatient as one pair). All the 20 pairs were then randomlyallocated by using split mouth system into two groups suchthat mini-implant placement was guided by CBCT on oneside and RVG (digital intraoral periapical radiograph) onthe other side in all the patients.All the patients were treated with a preadjusted edgewise

appliance of MBT prescription (0.022 × 0.028-in. slot). Asequence of aligning wires was used for leveling andalignment until a 0.019 × 0.025-in. stainless steel archwire could be passively engaged.After initial leveling and alignment, CBCT scans ( iCAT

Cone beam three-dimensional imaging system, ImagingSciences, Hatfield, PA, USA) were performed for all thepatients for the determination of the ideal site for mini-implant placement in the buccal interradicular spacebetween the second premolar and the first molar in maxil-lary and/or mandibular arches (with arch wires in place).CBCT scan was taken with the dosimetry parameters of120 kV, 37.07 mA, and 40 s scan time. Measurementswere performed by an expert oral and maxillofacialradiologist using iCAT vision software for bone density as-sessment and linear measurements and Digimizer (Version4.0, MedCalc Software, Ostend, Belgium) image analysissoftware for angular measurements.

Determination of ideal site for mini-implant placementOrthodontic arch wire in the second premolar and thefirst molar region was taken as a reference for all themeasurements (Figure 1a,b). Four bone measurementsnamely mesiodistal distance, cortical bone thickness,buccolingual thickness, and bone density were obtainedin the axial slice sections corresponding to the variousheights from the arch wire within the limits of mucogin-gival junction (Figure 1c and Figure 2). The level ofmucogingival junction in the second premolar and thefirst molar region was predetermined clinically, and itsdistance from the arch wire was also calculated.Based on the measurements performed by an oral radi-ologist, the vertical level with a maximum mesiodistal

Figure 7 Graphical representation of the height of mini-implants in CBCT group (in postplacement CBCT).


interradicular distance with optimum buccal corticalplate thickness, bone density, and buccolingual thicknesswas considered to be the ideal height for mini-implantplacement. Hence, ideal site for all the mini-implantswere identified (center of the mesiodistal space at thedetermined ideal height).However, this information was given to the operator

only for CBCT-guided side during the mini-implantplacement.

CBCT groupIn the CBCT group, the ideal sites as determined in theCBCT images were correlated clinically for the correctmesiodistal positioning of mini-implants at the desiredheight.

Determination of the point of entry of mini-implant clinicallyby using CBCT data

1. A perpendicular was dropped from the ideal point ofinsertion of mini-implant to the arch wire (in CBCTimage) (Figure 3a).

Figure 8 Graphical representation of the height of mini-implants in R

2. The distance of the point of intersection of theperpendicular on the arch wire to the distal end ofthe second premolar bracket was measured(in the CBCT image) (Figure 3b).� This distance was used clinically to mark the

mesiodistal positioning of the mini-implant onthe CBCT-guided side.

3. The ideal height for the mini-implant placement wasmarked intraorally as determined in the CBCT image.

The operator was trained by the oral and maxillofacialradiologist for interpreting the CBCT measurements.Based on the measurements derived, the operatorinserted the mini-implants at the identified sites underlocal anesthesia.

Digital intraoral radiography/digital RVG groupAn intraoral periapical view of the second premolar andthe first molar region with custom made guide [21] inplace using digital RVG (Kodak RVG 5100, Marne-la-vallée, France) was taken (Figure 4). The custom madeguide consists of two parts: a grid and a grid holder.

VG group (in postplacement CBCT).

Table 1 Comparison of mean deviation of mini-implantsfrom ideal position between CBCT group and RVG groupwith level of significance

Variable CBCT group(n = 20)

RVG group(n = 20)

Significance(p value)

Mean DMH (in mm) 0.0985 0.565 0.02*

Mean DMEP (in mm) 0.391 0.651 0.143

Mean DMT (in mm) 0.586 1.038 0.204

Mean DMA (in degrees) 4.7 6.2 0.624

*Significant difference in mean deviation of height of mini-implant (p < 0.05)DMH, deviation of height of mini-implant; DMEP, deviation of point of entry ofmini-implant; DMT, deviation of tip of mini-implant; DMA, angular deviation ofmini-implant from the ideal path.


This grid provided an option of nine cells and the areawhich seemed to be centered between the adjacent rootsand at an optimal height was identified as the site formini-implant placement. A bleeding point was createdwith the explorer through the guide. The guide was thenremoved and mini-implant was inserted at the identifiedsite under local anesthesia.All the mini-implants were inserted by a single operator.

Postplacement CBCTAfter insertion of the mini-implants, another CBCT scanfor comparative evaluation of the accuracy of the siteselection and mini-implant placement between the twogroups was performed by an expert oral and maxillofacialradiologist.The following parameters were observed in the

postplacement CBCT.

1. Height of the mini-implant from the arch wire(Figure 5)

Taan

Va

M

M

M

M

DMm

� Deviation of height of mini-implant (DMH) fromthe ideal height was determined.

2. Mesiodistal position of the mini-implant at theinterradicular area� The ideal path of insertion of the mini-implant is

drawn on the axial slice view and followingparameters were measured.

ble 2 Comparison of mean deviation of mini-implants from ideal pd RVG group with level of significance

riable CBCT group

Right side(n = 10)

Left side(n = 10)


ean DMH (in mm) 0.091 0.106 0.939

ean DMEP (in mm) 0.361 0.422 0.662

ean DMT (in mm) 0.756 0.079 0.256

ean DMA (in degrees) 4.6 0.2 0.873

H, deviation of height of mini-implant; DMEP, deviation of point of entry of mini-implant; DMini-implant from the ideal path.

i. Deviation of the point of entry of mini-implant(DMEP) (Figure 6a)

ii. Deviation of the tip of mini-implant (DMT)(Figure 6b)

iii. Angular deviation of the mini-implant (DMA)from the ideal path (Figure 6c)

3. Root contact of the mini-implant in the axial sliceview (Figure 6d)

Statistical analysisThe means and standard deviations for DMH, DMEP, DMT,and DMA were calculated for the mini-implants placed inboth groups. The data was tested for normality and itshowed a non-normal distribution. Hence, the comparisonof the means of DMH, DMEP, DMT, and DMA between thegroups and within each group was done by independentsamples Mann-Whitney U test (non-parametric test) witha p value of less than 0.05. Since the aim of the study wasto compare between the two groups, only the absolutevalues without ‘+’ or ‘−’ signs were considered.

ResultsThe heights at which mini-implants were placed in theCBCT group and RVG group are graphically representedin Figures 7 and 8, respectively, with an average height ofmini-implants being 6.85 mm in CBCT group and6.40 mm in RVG group. Mean values for DMH, DMEP,DMT, and DMA for the CBCT group and RVG groupalong with the comparison of these parameters aretabulated in Table 1. Statistically significant difference(p value = 0.02) was observed between the two groups formean DMH, with the deviation being 0.0985 mm in CBCTgroup and 0.565 mm in RVG group. Mini-implants wereplaced at a lower height (closer to the arch wire) in theRVG group. The differences in the mean values for DMEP,DMT, and DMA were statistically non-significant.Intragroup comparisons are depicted in Tables 2 and

3. No statistically significant difference was observed onthe right and left side and in the maxillary and mandibulararches in each of the groups.

osition between right and left side in CBCT group

RVG group

Right side(n = 10)

Left side(n = 10)


0.768 0.362 0.226

0.57 0.733 0.702

0.815 1.261 0.111

2.8 5.6 0.563

T, deviation of tip of mini-implant; DMA, angular deviation of

Table 3 Comparison of mean deviation of mini-implants from ideal position between maxillary and mandibular sites inthe CBCT group and RVG group, respectively, with level of significance

Variable CBCT group RVG group

Maxillary site(n = 12)

Mandibular site(n = 8)


Maxillary site(n = 12)

Mandibular site(n = 8)


Mean DMH (in mm) 0.0825 0.1225 0.256 0.65 0.436 0.354

Mean DMEP (in mm) 0.361 0.436 0.570 0.505 0.871 0.149

Mean DMT (in mm) 0.499 0.717 0.401 0.944 1.178 0.727

Mean DMA(in degrees) 4.416 5.125 0.683 4 9.5 0.099

DMH, deviation of height of mini-implant; DMEP, deviation of point of entry of mini-implant; DMT, deviation of tip of mini-implant; DMA, angular deviation ofmini-implant from the ideal path.


In this study, three out of twenty mini-implants in theRVG group showed root contact. Of the three root contacts,one showed proximity to the second premolar and twoshowed proximity to the first molar. All the three mini-implants which contacted the root surface were placed inthe mandibular arch and none of them showed any signs offailure during the loading period of 2 months.One mini-implant in the RVG group was removed within

the first week of loading due to increased mobility and,hence, was considered a failure. This failed mini-implantwas not in contact with any of the neighboring roots.

DiscussionThe importance of accurate mini-implant positioning can-not be overemphasized. Accurate mini-implant position-ing reduces problems such as loosening of the implant orinvasion of the sinuses, periodontal ligament, or root sur-face and facilitates the use of proper force vectors duringloading [22].In this study, CBCT scan, to assess the possible sites for

mini-implant placement, was done after preparatory ortho-dontic treatment unlike other studies [9-12] where CBCTscan was done prior to the treatment. Since the CBCT scanwas not routinely done for all the patients for orthodonticdiagnosis, hence, only after a confirmatory diagnosis pa-tients were included in the study and exposed to CBCT.Secondly, any change in the root position and crown inclin-ation during preparatory orthodontic treatment may inter-fere with the mini-implant positioning according topretreatment CBCT. Also, taking CBCT after preparatoryorthodontic treatment allowed the use of orthodontic archwire as a standard reference line. Measurements done in re-lation to this standard reference can be used clinically with-out the need of expensive surgical guides/templates.Alveolar crest and cemento-enamel junction were not usedas reference because these could not be seen and correlatedclinically.In the present study, the mini-implants in the RVG

group were placed at a relatively lower height (i.e., closer tothe arch wire) as compared to the ideal height determined,the mean (average) deviation being 0.565 mm. Consideringthe general guidelines for optimal sites for mini-implant

placement as quoted by Fayed et al. [8] and Poggio et al[23] in which a range of different heights are given formini-implant positioning, clinical relevance of the differencein height of mini-implants in this study is questionable.Considering the mean deviations in the mesiodistal directionnamely the mean DMEP, DMT, and DMA, results showed ahigher deviation in the RVG group, but the difference in thetwo groups was not statistically significant. And most of themini-implants in both the groups were placed within thesafe zone in the interradicular space.Root contact was defined as the contact of mini-implant

surface with the neighboring root in the CBCT images.Three out of twenty mini-implants in the RVG groupshowed root contact while others followed a path withvarying amounts of linear and angular deviation from theideal path without contacting the root surface. Accordingto a study by Lee et al. [24], peri-root space might not bean absolute parameter for mini-implant stability as move-ment of about 0.5 mm was detected even in stable mini-implants under loading [25,26]. Fortunately, it is not ne-cessarily detrimental even if the root is touched by thescrew because almost complete root repair has been re-ported from an animal study [27]. The biologic nature andthe osteodynamics around the orthodontic miniscrewunder constant load need to be elucidated further in thefuture.It is found that 15% of the mini-implants placed in the

RVG group had root contact while none in the CBCTgroup had root contact. On careful evaluation of thepostplacement CBCT, it was found that all the threemini-implants in the RVG group which contacted theroot surface were placed in the mandibular interradicu-lar space. The root contact may have occurred due tothe presence of narrower interradicular spaces in themandibular arches and reduced accessibility in the man-dibular posterior region [8,23].One mini-implant in the RVG group, which was removed

within the first week of loading, was not in contact withany of the neighboring roots but was placed relatively closerto the arch wire. On retrospective evaluation, it was con-cluded that the reason for the failure of the mini-implantcould be insufficient cortical bone thickness at the site of


mini-implant placement which is thought to be a key deter-minant for initial stability of mini-implant [28-30].The present study indicated no significant difference in

deviation from the ideal placement of mini-implantsbetween the right and left sides and between the maxillaryand mandibular sites in each of the two groups. Thisshows that the operator was not biased towards any siteduring the mini-implant placement procedure.From the above discussion, it can be stated that none of

the two methods were able to guide the mini-implantaccurately at the ideal position. However, most of themini-implants in both the groups were placed in a safezone without damaging the adjacent roots.Fabrication of surgical stents, guides, and templates

[9-12] is complicated, time-consuming, expensive, andrequired massive laboratory equipments and, hence, useof any of these latest technological advances for three-dimensional planning, and placement of mini-implants inthe CBCT group was not considered.Most clinicians use IOPA view of the region with a

surgical guide in place to identify the site for mini-implantinsertion. Hence, we used a grid in the RVG group inorder to simulate the routine protocol used by most of theclinicians. However, no guide was used during insertion ofthe mini-implants. From the observations of our study, itcan be concluded that the use of two-dimensional radio-graphs with a surgical guide is a more practical and cost-effective alternative to the three-dimensional planningwith CBCT for routine mini-implant placement.

ConclusionsThe following can be concluded from this study.

� Although CBCT provides accurate three-dimensional visualization of the interradicular space,two-dimensional intraoral radiographs seem toprovide sufficient information for mini-implantplacement.

� It is recommended for clinicians to use two-dimensionalradiographs with surgical guide for routine mini-implantplacement.

� Considering the high cost and higher radiation dose ascompared to two-dimensional radiographs, the routineuse of CBCT is not recommended for orthodonticmini-implant placement. However, if mini-implantplacement is difficult because of complex anatomy suchas an expanded sinus or alveolar bone loss, the use ofCBCT data for planning may be considered.

AbbreviationsCBCT: Cone beam computed tomography; DMA: Angular deviation of themini-implant from the ideal path; DMEP: Deviation of the point of entry ofmini-implant; DMH: Deviation of height of mini-implant from the idealheight; DMT: Deviation of the tip of mini-implant; RVG: Radiovisiography.

Competing interestsThe authors declare that they have no competing interests.

Authors' contributionsThe work presented here was carried out in collaboration with all theauthors. SK, TT, PR, and AK defined the research theme and designed thestudy. SK conducted the study, performed the literature review, interpretedthe results, and wrote the manuscript. TT was the chief supervisor of thestudy and provided guidance in every phase of the study and the writing ofthe manuscript. PR guided in statistical analysis, interpretation of data, anddiscussion of the study. AK guided in the statistical analysis andinterpretation of data. All authors read and approved the final manuscript.

Received: 9 June 2014 Accepted: 24 October 2014

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doi:10.1186/s40510-014-0061-xCite this article as: Kalra et al.: Evaluation of orthodontic mini-implantplacement: a CBCT study. Progress in Orthodontics 2014 15:61.

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